Excimer lasers use a lasing species that is an electronically excited, unstable compound that dissociates immediately after the lasing transition. A promising visible wavelength excimer laser uses XeF operating on a particular lasing transition that is referred to in the trade as the C.fwdarw.A transition (the letters C and A being conventional references to particular states of the excimer), and produces radiation in a broadband centered at a wavelength of about 486 nm. The prior art has used a gaseous mixture comprising a buffer gas, such as argon for example, together with a small amount of xenon and a donor gas which provides the necessary fluorine atoms. Most work has been done with NF.sub.3 as the halogen donor gas, although F.sub.2 has also been used.
Electrical excitation in the form of high-energy electron beams or electric discharges has been used to excite the XeF(C.fwdarw.A) laser in the art, but these methods have suffered from severe disadvantages that have limited their potential. In particular, the intense electrical excitation required to produce a sufficient number of excited XeF states results in a very large electron concentration but the electrons mix together the B and C states of the XeF excimer, thereby providing a channel for a competing reaction (B.fwdarw.X) that drains away excited states before they can provide the desired CX.fwdarw.A lasing transition. Also, electrical excitation results in large concentrations of ionized and excited species related to the mixture constituents (e.g., Xe**, Ar**, Xe.sub.2 *, Ar.sub.3.sup.+ . . . ), several of which absorb within the wavelength range of the C.fwdarw.A transition, thereby limiting the net gain of the laser and severely limiting the buildup of optical flux in the laser cavity. Photolytic pumping of XeF.sub.2 containing mixtures has been used successfully to minimize these effects, but the necessary apparatus required adds considerably to the complexity of the systems.